Dec 26, 2013 5:07 PM

Hi guys I'm new here and have been desperate to have a few rocks identified for a while now. It's started when I found what looked like a glittery pearl about 1cm in diameter inside what looked like flint off brownsea island. I have put pics below.

Then I was in lanzarote and wondered what this red in lava is? Hematite?

Then on the south coast of Spain I found these shiny rocks - white one like milky quartz but wondering if it was feldspar? Then the blueish coloured one again wondering if feldspar?

Finally today on a walk in the woods in Buckinghamshire I saw a piece of flint with a red centre like I've never seen before. I took it home and gave it a clean up and the centre of the red patch is again very shiny like crystals (similar shine to the first find mentioned). Any ideas?

Can I also add that the pearl looking one that appears in the last pic (they uploaded back to front I think) is what the pearl ball looks like after I managed to get rid of as much flint as possible. There is just a little flint on the top and bottom. The pearl ball is rock solid, I even took a hammer to it and its unbreakable!

In the order listing in the posting (I know it is infuriating how the system loads them in reverse order!)

1. Flint with quartz crystals inside (different forms of the same stuff). the slight pinky hue (your 'red') may be due to some iron contamination. That sort of crystal formation usually occurs in narrow fissures - along one of which your specimen broke.

2. Looks like a leucogranite of some sort (mainly feldspar and quartz with a bit of mica). Without mineralogical analysis, one can't say much more, eg. can't say if it is actually a granodiorite rather than a true granite.

3. I see reflective surfaces, but I can't tell if they're due to mica or just crystal faces on some other mineral species. The white colour is ambiguous: could be a white feldspar (sodium- or calcium-, as opposed to potassium- feldspar), but there are plenty of other candidate minerals.

5. Really don't have enough to go on (can't see any characteristic form, nor crystal faces, etc.). Any resemblance to a pearl is accidental; the shape and colour is not particularly significant; it is just a small piece of rock most of which is white; it looks like milky quartz (hence it may be quartzite or part of a quartz vein).

- we suspect quartz and Na-Ca-feldspar, which are fairly similar in hardness, especially considering that it would be difficult to know the exact hardness of any steel you were to use in comparitive hardness testing;

- confidence in the test can be degraded where specimens are composed of multiple small crystals/grains rather then large crystals. That's because what can appear to be a crystallographic scratch may be just a mechanical ripping out of small grains/crystals.

Macroscopic tests such as scratch hardness often need to be done in conjunction with other macroscopic analysis if an ID of rock or mineral is to be made. Density and reaction with acids can be helpful, eg.

The best means of reliable ID comes from microscopic analysis, using thin sections (thin enough to be translucent to transmitted light), and in part using polarized light. That enables textures and minerals to be identified fairly well. But ambiguity can remain, requiring further analysis using such means as X-ray diffraction and mass spectroscopy.

Thanks Mike! I have uploaded a few more of the pearl ball I keep referring to - its super hard, it won't scratch, nor shatter, it's harder than your average quartz, probably due to its spherical shape, but its intriguing nonetheless! Just wondered if it could be anything else! I have also uploaded another photo of the flint through the magnifying glass - if you can zoom in the top right area you can see what looks like sand mixed with tiny pieces of brown shattered glass that reflect light, just what it looks like.

So in order of mentioning in the first post you think:

1. Pearl ball that was inside flint is crystallised milky quartz

2. The red core of the lava segment - not enough to go on

3. Spanish white milky quartz/ feldspar -Not enough to go on

4. Spanish blue hue rock - possibly leucogranite

5. Quartz with red area of crystals - quartz in flint with iron

Is that all right? If I did want to take any specimens anywhere to get them looked at, where could I take them any ideas? I'm not referring to these, but to other rocks I have that I would like to know what they are.

You say the 'pearl ball' was inside the flint. How do you mean 'inside'? Was there a cavity open to the atmosphere? Was there a cavity that was not apparent until you broke the flint? Was there no cavity; the specimen just being part of the interior of the flint that became apparent when you broke it? Etc.

Your further photo of 5 doesn't really shed any extra light. I can see grey clay or other fine particulate material in some of the crevices, that's all. Oh I should mention there appear to be fossil shell fragments in it (visible in your original photo). Flints often contain fossils.

You may find these interesting re flint / chert / other micro/crypto-crystalline forms of quartz:

Thank you Mike for all that super info. I didn't realise the flint had fossil shell in it!

Re the pearl ball, I have made a small illustration but I'm far from an artist! It was visible on either side of the flint 'shell' it had, and was obviously glittery, which I thought may be the sea salt crystals. It's a definite ball, it had no other similar quartz like material anywhere near it, and it was surrounded by an orange coloured rock which was the latest layer on the surface and within that there was also flint.

So it was almost exactly like the earth, a pearly glittery (quartz) ball, surrounded by flint, surrounded by orange new casing. The ball poked through either sides of the rock itself, it looked like the two sides leaving the rock visible had already broken away.

Some flints are geodes - that is, they have a hollow in the middle, and that may be lined with quartz crystals. Sometimes, geodes have loose fragments within them. The hollow in a geode can be various shapes, some quite irregular, with protrusions that can become detached (or not). What goes on in inside a geode is somewhat mysterious: slow (geological time scale) chemical processes can result in deposition and solution of solids in various ways. I think your flint was a geode of sorts, including your pearl as a protrusion, covered with quartz crystals; it could even represent a fossil. Such a fossil could have been completely replaced by the processes of solution and deposition, or it might persist in the centrre of your 'pearl'.